'88 240 fuel pump relay not switching on

I'm trying to figure out a problem with an '88 240 that I bought to put
a V8 into.

I needed to start it to shift it around the yard but it just wouldn't
start. The fuel pumps weren't running and there was no power at the
in-tank pump fuse.

Okay, thinks I. I'll grab the fuel pump relay from an '82. Plugs in
the same but the pins are completely differently labelled. That's not
good...

So I popped the case off the '88 relay and got a big surprise. There
were no electronics, just 2 relays and a diode. Okay...

Plug the relay back in with the cover off, leaving it dangle under the
dash so that I could watch the contacts.

Turn the ignition on. One relay of the two clicked in and straight
back out. The other didn't move. Switch off the ignition and switch it
back on. This time, neither relay moved. Hmm.

Switch ignition on and push the relay armature in with a finger. Crank
engine, fires and stalls. Do it again and the engine runs. Let go of
the relay and it stays on.

Given that one relay didn't move and the other couldn't pull in but
could hold in, I'm guessing that the problem is probably in the relay
unit rather than the EFI output that drives it.

Is this common on these late model relays, or is it more likely to be a
fault in the driver circuit in the EFI computer?

I'm assuming that the 2 relays are separate units for the main and
in-tank pumps as with earlier models? If so, I was probably running it
on main pump only.

 

The 2 relays are the fuel injection main relay (powers computer etc),
the second is the fuel pump relay (powers both pumps, the prepump
through an additional fuse). The driver circuit for the fuel pump relay
is a common failure, but usually it's dead, not weak. A new relay would
be an easy, and relatively cheap test.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

That's wierd.

I ran the thing with only one of the relays on. I figured that it was
probably just running the main pump without the in-tank pump.

Replacing the unit is of little value to me now, as the entire engine
and injection system will be coming out soon to fit a 350 chev on LPG,
hopefully complete with twin turbos.

I just need to run it occasionally to shift it around the yard to mow.